A temperature fuse has conventionally been used for protection against overheat damage of domestic or industrial electronic and electric devices. A temperature fuse has been used in various household electrical appliances, portable devices, communication devices, office equipment, car-mounted devices, AC adapters, chargers, motors, batteries, and other electronics as protection components for promptly disconnecting a circuit in case of abnormal overheat. In general, a temperature fuse has a wide nominal rated current approximately from 0.5 A to 15 A, however, in particular for a high current not lower than 6 A, a temperature-sensitive pellet type temperature fuse which has a contact, senses an abnormal temperature, and causes the contact to perform an opening operation is suitably made use of.
Temperature-sensitive pellet type temperature fuses in a variety of forms in terms of details are available, and for example, a temperature-sensitive pellet type temperature fuse described in WO2003/009323 (PTD 1) or Japanese Patent Laying-Open No. H08-045404 (PTD 2) is in such a form that a metal case, a pair of leads, an insulating material, two springs which are tightly and weakly compressed, a sliding electrode, and a temperature-sensitive material are provided as main components and the sliding electrode is movable while it is in contact with an inner surface of a conductive metal case. The weakly compressed spring is provided between the sliding electrode and the insulating material and the tightly compressed spring is provided between the sliding electrode and the temperature-sensitive material. In a normal state, these compressed springs are both in a compressed state, and the tightly compressed spring is stronger than the weakly compressed spring. Therefore, the sliding electrode is biased toward the insulating material and in contact with one lead, such that the sliding electrode can be rendered conductive. Therefore, as this lead is connected to a wire of an electronic device or the like, a current passes from the lead through the sliding electrode to the metal case and then to another lead.
An organic substance, or a thermosoluble substance or a thermoplastic substance such as a thermoplastic resin, can be employed for the temperature-sensitive material. When a prescribed operating temperature is reached, the temperature-sensitive material is molten or softened and deforms under a load from the compressed spring. Therefore, when an electronic device or the like to which the temperature fuse is connected is overheated and the prescribed operating temperature is reached, the temperature-sensitive material deforms, the tightly compressed spring is unloaded, and the weakly compressed spring is released from the compressed state in response to extension of the tightly compressed spring and extends. Thus, the sliding electrode moves while it is in contact with the inner surface of the metal case away from the lead, and passage of the current is cut off. By connecting the temperature-sensitive pellet type temperature fuse having such a function to a wire of an electronic device or the like, breakage of a main body of a device, fire, or the like due to abnormal overheat of the device can be prevented in advance.
As a sliding electrode used in the temperature-sensitive pellet type temperature fuse, for example, a sliding electrode obtained by rolling a metal material in a thin plate shape and working by press-forming the plate is generally employed. For a sliding electrode used in the conventional temperature-sensitive pellet type temperature fuse, a single material composed exclusively of silver or a silver alloy alone has been used for the necessity of prevention of welding of a contact due to an arc caused during an operation of moving away from a lead. However, it has not been economical, because a relatively large amount of silver representing a noble metal is consumed.
Japanese Utility Model No. 3161636 (PTD 3) proposes such a construction that a sliding electrode made of a copper material is coated with extremely thin silver plating. The coating with extremely thin silver plating, however, tends to be broken by an arc or the like caused during an operation of moving away, and in this case, a surface of the copper material is exposed to cause welding of a contact. Therefore, welding of the contact could not sufficiently be prevented. If a contact is welded, a current is not disconnected and a function as a temperature fuse is not achieved. In addition, plating is poor in adhesiveness to a base, and there has been a problem of peel-off or the like.